So, I have a new user, he is registering on the webpage for a one year membership that costs 30 EUR, he puts in his data, then he get's to see his basket, then he selects as payment method "offline" and then he get's to see this button where he has to confirm that he is paying offline.

After he is pressing this button he will see on top of the page the following error (above his payment slip):

A payment invoice exists already: Please check below if it is correct. If not correct, click on the cancel link below, and select your choice again.

The problem was originally discussed about 6 month ago here:

www.joomlapolis.com/forum/255-developer-members-support/234051-updating-cb-1-9-1-to-4-0-12-and-cbsubs-3-0-0-to-4-1-0?start=42#283902